Question
what can we do to get rid of weeds and keep our St. Augutine in good shape. also, grass thinning in shaded areas need help

Answer
First, let's go to your thinning Grass problem.

I can tell you that of the Warm season Grasses, St Augustine Grass generally takes more shade than other Warm season Grasses.  In DENSE shade, however, it will still be weak and spindly.

Some kinds of St Augustine do a little better in shade than others.  So we have to find one that is the  best for you.
NONE of these will thrive without at least 6 to 7 hours of full sun.

Let's look at the University of Florida Coop Extension website:

http://edis.ifas.ufl.edu/LH010

for the latest word on Florida shade Grass, 'St Augustinegrass for Florida Lawns'.  They list some top shade
performers: Dwarf varieties AMERISHADE; BITTERBLUE, CLASSIC, DELMAR and SEVILLE.

Worst for shade: FLORALAWN and FLORITAM (which Univ of Fla points out is 'the most widely produced and used St Augustinegrass in Florida' -- my guess is you have tried this one).

This grass is almost always grown with sod, plugs or sprigs. It spreads and grows by using stolons -- stems above the ground -- at the leaf nodes.  So when it grows, St Augustine creeps along the ground.

Now, any list you look at, Mike, of Grass to Grow is going to be packed with a lot of warnings about Chinchbugs, diseases and Grass health problems.  The most important variable for you -- the ONLY important variable for you -- is going to be your sun situation.  You want a Grass that grows in partial shade.  I can help you with all the
other problems.  In fact, I can tell you how to keep from getting them.  That step begins with your promise not to let anyone put down a 'Weed control' or a 'grubkiller' or 'chinchbug killer' or 'fungicide' WITHOUT THE APPROVAL OF THE LONG ISLAND GARDENER.  Because these are almost always worse than other things you can do.  They just are not very profitable.  And most people don't want to think about them.

But be realistic about your shade.  How much shade do you have where that Grass is thinning?  Tell me, please.

Now, let's go to your Weed problem.

St Augustine generally does not have this problem.  Thick healthy St Augustinegrass has way too much muscle for booting out uninvited Crabgrass, Creeping Charles, Dandelions, etc.

Tell me, how were you mowing this Grass this Summer?  Was this done weekly, or daily, etc?  Any fertilizer that went down there one day?  Any traffic in the Brown area?

rsvp and thanks for writing.